How to switch back to default view after switching to camera view in blender 2.92
I don't know if I understand the question, but the hints given here with switching the layout and using the pie menu make me think I'm completely wrong. What I read in your question is, you were navigating in the 3D Viewport and hit Ctrl+Alt+Numpad 0. This is the shortcout for Align Active Camera to View. This means, your camera is aligned to what you see in the viewport in that moment and this is the new camera view.
Usually you only have to press Numpad 0 to switch between Camera Perspective and the normal navigation view, the User Perspective. Let's say the camera's looking on the left side of an object, and you navigate your view to the right side. Numpad 0 switches between left and right side view.
My problem is now to understand what you exactly want. Numpad 0 gets you to camera view and back to what it was before, you can toggle between them. This doesn't work if you move the viewport when in camera view, because it exits Camera Perspective and becomes the new User Perspective.
If however your camera is now looking differently at the scene than before, that's because you used Ctrl+Alt+Numpad 0. This moves the camera to a different location and rotation to fit the Camera Perspective to the active User Perspective. Switching views doesn't get your old camera view back because your camera is no longer in the same location as it was before.
To get it back the only thing you can do is Undo your action with Ctrl+Z, but as all undo actions this only works as long as you didn't do too much inbetween or didn't close and re-open your file.